Drying process and spray dryer for carrying out the process

ABSTRACT

Apparatus and method for drying suspensions, solutions and free flowing materials in a drying chamber in a cylindrical housing wherein the material is fed directly into the inlet against a rotating impeller and a scraping means is used against a rotating drum surrounding the impeller which limits the size of the drying chamber, the dried material moving past a displacement element within the drum which curves out conically from the impeller toward the end of the cylindrical housing.

United States Patent [191 5/1956 Rothe 34/58 Koller July 3, 1973 I DRYING PROCESS AND SPRAY DRYER FOR 2.716.290 8/1955 Irving 34/58 CARRYING OUT T PROCESS FOREIGN PATENTS OR APPLICATIONS Inventor: Hans o u e z. Switzerland 363,941 9/1962 Switzerland 34/8 [73] Assignee: Buss AG, Basel, Switzerland Primary Examiner-John J. Camby [22] F'led: Attorney-Abraham A. Safi'itz [21] Appl, No.: 168,117

I [57] ABSTRACT [30] Foreign Application Priority Data Apparatus and method for drying suspensions. solu- Aug. 5, I970 Switzerland l I875/70 and free Wing materials in a drying chamber in g v a cylindrical housing wherein the material is fed di- 521 vs. c|...'..,..'..,.' 34/8 recfly imo the inlet against a rotating impeller and a [51] Int. Cl. F26b 5/08 Scraping means is used against a rotating dFum 5s 1 Field of Search 34/8, 58 rounding the impeller which limits the size of the y g chamber, the dried material moving past a displace- 5 References Cited ment element within the drum which curves out coni- UNITED STATES PATENTS cally from the impeller toward the end of the cylindrical housing. 2,634,512 4/l953 Irving 34/58 2,744,338 13 Claims, 1 Drawing Figure The present invention refers to a drying process as well as to a spray dryer for the drying of suspensions, solutions, pasty materials and free-flowing or similar materials. The drying process is carried out in a drying housing, in which an axial flow of a drying medium prevails on the periphery. Accordingly the spray dryer exhibits a cylindrical housing with an inlet for the drying medium at one end and an outlet for the dried material and for the drying medium at the other end.

sharing the same axis with the housing, an impeller 7 is arranged which rotates on shaft 8 of a driving mechanism 9. The driving mechanism 9 is located inside housing 1 on the opposite side of the impeller to the tube- The proposed process and the spray dryer are ini tended to be suitable for the widest variety of materials,

press or filter cake as long as these materials could not be conveyed with gear or screw-type pumps. Thus these materials had to be kept pumpable, which of course had a negative effect on the drying process. In addition, all known spray dryers have a further disadvantage in that they require a great deal of space.

The purpose of the invention is to avoid the described disadvantages and to propose a process as well as a spray dryer which are universally applicableand which permit an advantageous combination with afterdryer's as well, for example for subsequent vacuum dry- The process for the drying of suspensions, solutions,

, pasty materials and free-flowing materials'in a housing within which an axial flow of the drying medium prevails on the periphery is, according to the invention, characterized by the fact that the material to be dried is fed under pressure directly into the drying housing parallel, to, but outside the flow of, the drying medium, is there reduced in size and is carried radially at increased speed directly into the flow of drying medium.

ln this way, even materials having very high viscosity can be dried without problems.

' The spray dryer according to the invention,-for carrydrying space and against-the inner surface of-which scraping devices can be applied.

on the attached drawing, an execution example of the object of the invention is illustrated.

The, spray dryer for the drying of suspensions, solutions, pasty materials and free-flowing materials-exhibits a cylindrical housing 1,-the axis of which'runs horizontally, and which is equipped with a cooling jacket on its surface. The front end 3 of the housing is provided with an opening, through which a horizontal hollow shaft is introduced, this shaftextending into the inside of housing 1 and serving to accept a tube-shaped casing 5 with screw conveyor 6. Inside housing 1 and shaped casing 5. in accordance with the proposed invention, the inner end of the tube-shaped casing 5 extends into the impeller 7, so that materials which are not pumpable and which are difficult to convey are fed directly to impeller 7 by means of screw conveyor 6. This is not possible with present spray dryers, which are only suitable for pumpable pastes. v

Thefend of the hollow shaft 4 which is located within housing 1 carries a drum 10, which can be arranged to rotate or to be stationary. In the execution example shown, drum 10. rotates together with hollow shaft 4, which carries a driving gear wheel 11 and which is driven by means of chain 12. The detailled design of the chain drive is not illustrated in the drawing and can be executed in known fashion.

The front end 3 of housing 1 is provided with a hotair supply line 13 and the cylindrical surface at the end opposite to front end 3 is provided with an outlet 14, through which the dried material is removed from the drying space in the form of an air suspension.

On the edge of the inner surface of drum 10, the outlet rim is formed as a baffle ring 16, and in drying space 15 there is a displacement element 15 which is shaped as a cone, in that it widens out from impeller 7 toward the end of cylindrical housing 1, and which simultaneously serves to accept the driving mechanism 9. l8 designates a guide bafr'le of the displacement element 17.

Provided further in the area of the inner surface of drum 10 are lamellar scraping knives 19, which are formed as springs and which are mounted in a frame 20 of a vibrator 21.

The material to be dried is introduced through the tube-shaped casing 5 by means of screw conveyor 6 directly to impeller 7 in axial fashion; the impeller shreds it and slings it away finely divided. In this way it is even:

5 possible to dry highly viscous dyestuff pastes, which results, in contrast to the conventional vertical arrange ment, in the residence time of the large material particles in the drying space being rather longer than the residence time of the smaller particles, which is desirable and which provides a better drying. In a vertical dryer arrangement, the larger, more difficult to dry part-icles fall more quicklythrough the drying space than. the light particles and hence are dried less. thoroughly.

In the operation of the proposed spray dryer, the particles leaving the impeller 7 fly against the inner wall:of the drum l0,- and the danger exists that they will stick there and bake on. In order to avoid this, the lamellar scraping knives 19 are provided, against which the drum rotates. It is possible as well, however, to take the opposite approach and to arrange the scraping knives to rotate while the drum remains stationary. Since the scraping knives consist of individual resilient layers,

they are capable of adjusting to unevenness inthe drum surface. A further improvement of the scraping effectiveness is achieved by causing the knives to vibrate by means of the vibrator 21, or, for example, by pressing them against the drum wall from the outside with springs. Finally, it should be noted that the frame 20 can be fastened to the displacement element 20 by means of brackets 23. Y

The drum itself can be manufactured quite simply from un-machined, cylindrically-rolledplate; any imbalance has only a nagligible effect on the drum bearmg.

In order to prevent scorching of the material, the drum surface is cooled with cold air, which is supplied through a separate line 24 containing a throttling organ 25. Afterwards, the heated cooling air is mixed together with the drying air and fed to the drying space.

Very important to the drying is the introduction. of the drying air through the line 13 into the drying space 15. It is advantageous to generate a rotating turbulence by tangential air entry or by the use of a paddle cascade 26. In this connection it should be observed that a rotational turbulence with too high a flow velocity will cause poor intermixing of the material and its impingement on the drum wall through centrifugal force, while too slow a rotation flow is likewise of no use, since the product will not be sufficiently whirled up. In order to permit the conditions of a rotational turbulence to be fulfilled under various kinds of operating conditions, the described spray dryer is equipped with a paddle cascade arrangement, on which the paddle angle and pitch are adjustable by means of washers. Large cascades are divided into two or more sections, whereby the individual sections can be operated with different air temperatures. For instance, cooling air can be blown in through the outermost section in order to treat a product particularly gently.

ln rotational flow, a velocity gradient is established from the inside outwards, so that the static pressure on the inside becomes lower, resulting in a superimposed current flowing from the outside inwards. This means that the air in the core of the turbulence no longer has a chance to give off its heat to the material being dried. To avoid this disadvantage, the arrangement of the displacement element 17 is proposed, which guides the air in the core of the turbulence towards the outside.

The mentioned baffle ring 16 brings a further advantage, -in that the material is held back, extending the residence time and improving the intermixing of air and material.

To prevent undesired turbulences, which could move the material counter to the main direction of flow and possibly lead to crusting of the paddle cascade, the drying space is subdivided into two parts. In the front part, the undisturbed rotational turbulence prevails; in the rear part, the flow is disturbed by the exhaust through the outlet line 14. The mentioned screening off is achieved through the conical shape of the displacement element 17, through the baffle ring 16 and through the guide baffle 18 in the neighborhood of the outlet opening .14. 7

It is also of importance that the proposed scraping knives 19 do not disturb the flow. They should be as small as possible and should run as parallel as possible to the drum wall.

In order to simplify the cleaning of the equipment, the end flange 27 can be connected to housing 1 by means of a snap closure. The end flange, .which supports the displacement element 17 and the organs 9 and 21, is then itself supported separately by a swivelling mount.

As an alternative execution, if required, the driving mechanism 9 can be mounted on the material in-feed vantageously with an after-dryer. Hence the heat losses provement in which said impeller (7) rotates about a are reduced to advantage, and improved safety against the dreaded dust explosions and detonations, since the smaller volume makes possible an efficient, pressuretight construction, for which smaller openings for overpressure protection are sufficient.

1 claim:

1. In a spray dryer for drying suspensions, solutions, pasty materials and free-flowing materials having a cylindrical housing with an impeller arranged within said housing and a drying chamber inside the housingwith an inlet at one end for the drying medium and an outlet at the other end for the material to be dried, the imhorizontal axis (8), a feeding device (5,6) preceeding the inlet for feeding the material to be dried and leading said material directly into the impeller (7), a rotating drum (10) arranged within the housing, which limits said drying chamber (15), scraping devices (19) which can be applied against the surface of said drum and a displacement element (17) arranged within the drum (10) which widens out conically from the impeller (7) toward the end of the cylindrical housing (1).

2. Spray dryer according to claim 1 wherein the feeding device comprises a tube-shaped casing (5) and, arranged inside thecasing, a screw conveyor (6) leading all the way to the impeller (7).

3. Spray dryer according to claim 1 wherein the driving mechanism (9) is located inside the housing (1) on the opposite side of the impeller to the tube-shaped casing (5).

4. Spray dryer according to claim 1 wherein scraping knives (19) work in conjunction with the inner surface of the drum (l0).

5. Spray dryer according to claim 1 wherein the scraping knives (19) are connected to a vibrator (21), whereby the scarping knives are pressed on with spring pressure.

6. Spray dryer according to claim 1 wherein the internal surface of the drum (10) is equipped with a baffle ring (16). p

7. Spray dryer according to claim 1 wherein, in the neighborhood of the outlet line (14), the displacement element (17) is provided with a guide baffle (l8).

8. Spray dryer according to claim 1, wherein the scraping knives (19) are fastened adjustably to the displacement element (17) by means of brackets (23).

9. Spray dryer according to claim 1, wherein the housing (1) is equipped with a cold air line (24) for cooling the drum surface.

10. Spray dryer according to claim 1, wherein the end of the drum (10) at the point where hot air enters,

pasty materials and free-flowing materials comprising the steps of, leading the materials into a feeding device into a drying chamber within a cylindrical housing with an inlet at one end for the drying medium and an outlet at the other end for the material to be dried, that improvement which consists of, directing the material against a rotating impeller with in a rotating drum 10) arranged within the housing, which limits said drying chamber (15), while applying scraping devices (19) which can be applied against the surface of said drum and passing the material past a displacement element (17) arranged within the drum (10) which widens out conically from the impeller (7) toward the end of the cylindrical housing (1 

1. In a spray dryer for drying suspensions, solutions, pasty materials and free-flowing materials having a cylindrical housing with an impeller arranged within said housing and a drying chamber inside the housing with an inlet at one end for the drying medium and an outlet at the other end for the material to be dried, the improvement in which said impeller (7) rotates about a horizontal axis (8), a feeding device (5,6) preceeding the inlet for feeding the material to be dried and leading said material directly into the impeller (7), a rotating drum (10) arranged within the housing, which limits said drying chamber (15), scraping devices (19) which can be applied against the surface of said drum and a displacement element (17) arranged within the drum (10) which widens out conically from the impeller (7) toward the end of the cylindrical housing (1).
 2. Spray dryer according to claim 1 wherein the feeding device comprises a tubeshaped casing (5) and, arranged inside the casing, a screw conveyor (6) leading all the way to the impeller (7).
 3. Spray dryer according to claim 1 wherein the driving mechanism (9) is located inside the housing (1) on the opposite side of the impeller to the tube-shaped casing (5).
 4. Spray dryer according to claim 1 wherein scraping knives (19) work in conjunction with the inner surface of the drum (10).
 5. Spray dryer according to claim 1 wherein the scraping knives (19) are connected to a vibrator (21), whereby the scraping knives are pressed on with spring pressure.
 6. Spray dryer according to claim 1, wherein the internal surface of the drum (10) is equipped with a baffle ring (16).
 7. Spray dryer according to claim 1, wherein, in the neighborhood of the outlet line (14), the displacement element (17) is provided with a guide baffle (18).
 8. Spray dryer according to claim 1, wherein the scraping knives (19) are fastened adjustably to the displacement element (17) by means of brackets (23).
 9. Spray dryer according to claim 1, wherein the housing (1) is equipped with a cold air line (24) for cooling the drum surface.
 10. Spray dryer according to claim 1, wherein the end of the drum (10), at the point where hot air enters, is formed by a paddle cascade construction, in which paddle angle and paddle pitch are adjustable by means of washers.
 11. Spray dryer according to claim 10, characterized by the fact that the paddle cascade construction is divided into a number of sections for the introduction of drying air of differing conditions.
 12. Spray dryer according to claim 1, wherein the driving mechanism (9) of the impeller (7) is arranged on the side opposite to that of the material feed.
 13. In a process for drying suspensions, solutions, pasty materials and free-flowing materials comprising the steps of, leading the materials into a feeding device into a drying chamber within a cylindrical housing with an inlet at one end for the drying medium and an outlet at the other end for the material to be dried, that improvement which consists of, directing the material against a rotating impeller with in a rotating drum (10) arranged within the housing, which limits said drying chamber (15), while applying scraping devices (19) which can be applied against the surface of said drum and passing the material past a displacement element (17) arranged within the drum (10) which widens out conically from the impeller (7) toward the end of the cylindrical housing (1). 